<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>盒子模型</title>
    <style>
        * {
            box-sizing: border-box; /*设置为边框模型*/
        }

        .big {
            height: 500px;
            width: 500px;
            border: 1px solid red;
            left: 50px;
            /*top: ;*/
            /*padding: 150px;*/
        }

        .small {
            /*box*/
            height: 200px;
            width: 200px;
            border: 1px solid gray;
            margin: 150px;
        }
    </style>
</head>
<body>
<div class="big">
    <div class="small">

    </div>
</div>
</body>
</html>